This invention relates to welding torches, and more particularly to such torches incorporating non-consumable electrodes, typically of tungsten.
Tungsten inert gas (TIG) welding torches conventionally comprise a body portion in which is housed an elongate tungsten electrode one end of which projects from the body portion for welding purposes.
More particularly, the tungsten electrode is held in a split collet, itself housed within the body portion of the torch, the split tip of the collet being received within a tapering bore such that, when the collet is pushed forwards within the bore, the split tip thereof is urged into clamping engagement with the electrode to hold the electrode in its operative condition.
Conventionally, the split collet is pushed forwards by means of a threaded plug or backstop which is screwed into the body member to react against the rear end of the collet.
Ideally, the projecting tip of the tungsten electrode should not touch the parent metal during the welding process. However, in practice, and primarily because welding is a manual process, there is often contact, the electrode becomes contaminated, and it is necessary to remove the electrode from the torch, either to grind off the contamination or to replace the electrode.
In theory, when the threaded backstop is partially unscrewed within the body portion, the clamping effect of the split collet on the electrode should be released, whereby the electrode can be pulled out of the ceramic nozzle end of the body portion by the user""s gloved forefinger and thumb.
However, in practice, the heat generated during the welding process is often such that the split collet becomes adhered to the tungsten electrode, whereby unscrewing of the backstop does not release the split collet from the electrode, and the electrode cannot be removed from the torch other than by completely dismantling the torch.
Clearly this is a tedious, time consuming and inefficient exercise, which can also be painful to the operator because the torch assembly is extremely hot.
Furthermore, it is difficult to ensure that the decontaminated or replacement electrode is accurately positioned in the body portion when the torch is hot.
U.S. Pat. No. 3,097,290 discloses a welding torch substantially in accordance with the pre-characterising clause of claim 1.
It would be desirable to be able to provide a welding torch in which the non-consumable electrode thereof was more readily handleable than heretofore.
According to the present invention there is provided a welding torch comprising a body portion in which is housed, and from one end of which projects the tip of, an elongate, non-consumable electrode, clamping means within the body portion for releasably gripping the electrode, a plug member selectively movable between a first position in which the clamping means hold the electrode in an operative position, and a second position in which the clamping means are released from the electrode, and an ejector mechanism which, with the plug member in its second position, can be actuated to move the electrode axially within the body portion, characterised in that the ejector mechanism comprises a slide member mounted in the plug member to be axially slidable therein, and a push rod mounted to the slide member to extend axially therefrom and through the plug member into the body portion, the push rod being co-axial with the electrode and adapted to engage the end of the electrode remote from the tip, whereby, with the plug member in its second, release position, the slide member and push rod can be moved axially within the plug member and the body portion to move the electrode axially from its operative position.
In a preferred embodiment of the invention, the clamping means comprises a split collet surrounding an intermediate extent of the electrode and having a foremost operative position within the body portion clamping the electrode and a release position axially rearwards of the operative position.
Conveniently the plug member is screwed into the body portion and has a first, operative position in which an end face thereof engages the split collet and urges the collet into clamping engagement with the electrode, and a second, release position rotationally displaces from the first position in which the end face thereof is displaced axially rearwardly of the first position to enable release of the collet from the electrode.
Preferably, the mounting of the push rod to the slide member is such that, for a given axial position of the slide member within the plug member, the push rod can be moved axially relative to the slide member.
Conveniently axial movement of the push rod relative to the slide member is achieved by rotation of the slide member within the plug member.
In one embodiment of the invention, the slide member is internally threaded, the push rod extending from an externally threaded head member housed within the slide member, the push rod extending through the plug member to be axially movable but non-rotatable relative thereto whereby, on rotation of the slide member within the plug member, the head member and push rod are moved axially relative to the slide member and plug member.